A massive coronavirus outbreak has been discovered at a detention center in southeastern Seoul, with the source of infection remaining unknown.

As of Monday morning, a total of 215 people -- including 185 inmates -- tested positive for the virus at the Seoul Dongbu Detention Center, according to health authorities, after some 3,557 inmates and staff members underwent testing on Friday.

District courts in Seoul are on alert as many of the inmates from the detention center are said to have attended trials, leading the National Court Administration to instruct courts across the country to delay or change dates of trials for cases not considered urgent.

Another case was also reported at the Seoul Detention Center in Uiwang, Gyeonggi Province, on Saturday. As of Monday, the detention center had tested 85 people who had come into contact with the patient.

Former President Park Geun-hye is currently at the facility serving a 20-year prison term over bribery and other charges.

While an epidemiological investigation is underway, how the virus spread at the Seoul Dongbu Detention Center remains a mystery.

Most of the cases were found in a prison ward where incoming inmates are admitted and isolated for two weeks before they are transferred to other awards at the detention center.

There are three places where inmates could have come in contact with the virus: when they have meals, when they exercise or receive visits, and when they go to the court for trials.

At the detention center, a maximum of seven people share one room and inmates are served and eat meals individually. Inmates who were recently admitted exercise in a separate space from those who have been at the facility for extended periods. When attending trial or prosecutorial questioning, inmates are escorted to prosecutors’ offices and courts by officers, and wait with other inmates in a room.

Former President Lee Myung-bak has been serving his 17-year jail term at Seoul Dongbu Detention Center since Nov. 2 after being convicted of corruption. He reportedly tested negative for the virus.

Korea added 926 new coronavirus cases Monday after seeing over 1,000 cases for the five previous days amid an ongoing third wave of COVID-19 infections across the country.

By Ock Hyun-ju (laeticia.ock@heraldcorp.com)